Heaters with an electric heating element, which are pushed over a body to be heated and are fixed there by clamping, are known from the state of the art. For example, such heaters are used in injection molding machines or in hot runner and distributor systems as a nozzle heater for heating nozzle bodies.
It is already known from the commercially available state of the art that a one-piece clamping jacket, which is in direct contact with the heating element or, e.g., if the heating element is embedded between an inner metal jacket and an outer metal jacket, is in indirect contact with the heating element, and which clamping jacket has, when viewed in the radial direction, mutually overlapping sections, between which a wedge mechanism operated with a screw is arranged, is provided around the heating element. If the screw is turned in one direction, the wedge mechanism is moved such that its height changes, which leads to an increase in the distance of the overlapping sections of the clamping jacket and leads to fixing of the heater on the body to be heated because of the essentially constant length of the clamping jacket. The turning of the screw in the other direction makes it possible again to loosen the clamping jacket.
The increased space requirement of the clamping mechanism in the radial direction due to the wedge mechanism is problematic in this heater with clamping jacket, because the individual nozzles to be heated are arranged in blocks in many cases, especially in hot runner nozzles, and there is only a relatively narrow, tubular channel, into which the heater must fit, between the nozzle and the block.
Heaters such as those disclosed, for example, in DE 200 15 016 U1 or DE 20 2011 003 451 U1 were developed especially for applications in which such an increased space requirement cannot be met. The heating element is arranged between an inner metal jacket and an outer metal jacket in these heaters and the heater has a gap passing through it in the axial direction. Further, clamping elements are provided, which interact with the outer metal jacket such that their displacement in the axial direction causes a change in the width of the gap in the circumferential direction and the fixation on the body to be heated is achieved thereby.
A major problem of these heaters is the operation of the clamping elements, which must be carried out, with the heater pushed over, e.g., in many cases within a narrow, tubular channel, which is accessible from one side only. For example, it is barely possible to loosen the clamping element again. It is likewise problematic, in case of heaters whose length makes it necessary to arrange a plurality of clamping devices one after another in the axial direction in order to guarantee a sufficiently close contact between the heater and the object to be heated, to configure these such that they can be clamped individually.